End fire directive antenna



1947' N. E. LlNDE NBLAD 2,425,887

' END FIRE DIRECTIVE ANTENNA Filed Sept. 30. 1942 'Z Sheat Sheet 1 4 INVENTOR M4: 5. Z/wuwauw.

. ATTOR N EY 1947- N. E. LINDENBLAD I F iRE DIRECTIVE ANTENNA 2 Sheets-Sheet 2 Filad Sept. 30 1942 gas 8 INVENTOR WW I N 2; u m 5m u Patented Aug. 19, 1947 2,425,887 END FIRE DIREGTIV E ANTENNA Nils E. Lindenblad, Rocky Point, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application September 30, 1942, Serial No. 460,201

10 Claims.

The present invention relates to directive short wave antennas and, more particularly, to end fire arrays in which all the radiators thereof are directly energized from a transmission line.

An object of the present invention is the provision of a highly directive end fire antenna array,

Another object of the present invention is the provision of an antenna array, as aforesaid, which is compact in size and is rugged, in construction.

Still another object of the present invention is the provision of an antenna, as aforesaid, which is particularly adapted to be mounted on an airplane wing.

A further object of the present invention is the provision of a transmission line structure for an antenna, as aforesaid, whereby the constituent radiator elements may all be energized with equal voltages in proper phase without setting up reflections in the transmission line.

The foregoing objects, and others which may appear from the following detailed description, ar attained in accordance with the principles of the present invention by provisions of an end fire array of a plurality of spaced radiators arranged parallel to one another in a single plane, which includes the direction of desired maximum response of the array. Each antenna element is connected to a common coaxial line so tapered that it remains non-reflective throughout so that each radiator is fed the same voltage. The eoaxial line and part of the radiators are enclosed within a plastic shield for weather protection.

The present invention will be more fully understood by reference to the following detailed description, which is accompanied by a drawing in which Figure 1 illustrates in side View an embodiment of the present invention, while Figure 2 illustrates an end view thereof; Figures 3 and 4 lustrate directivity patterns of the antenna shown in Figures 1 and 2, while Figure 5 is a directivity pattern of the antenna as shown in Figure l with a modified form of mounting which is shown diagrammatically in Figure 6, and Figure 7 is a curve illustrating the relationship of reflection versus frequency of the antenna shown in Figure 1.

One embodiment of the antenna of the present invention includes an end fire array of nine radiators 10, each a quarter wave lon and, in this case, spaced a quarter Wave apart. Other spacings may be used if desired. Each antenna element is connected to the center conductor I2 of a common coaxial transmission line l5. The center conductor I2 is tapered from one end to the other so that it remains non-reflective throughout and so that each radiator is fed with the same voltage, that is, conductor I 2 is reduced in diameter at the point of connection of each of the radiators l5 thereto. The decrease in diameter is such that the impedance of the radiator II! and the center conductor l 2 at each point is equivalent to the impedance of the transmission line as a whole, The inner conductor [2 of the transmission line is surrounded by an outer shell I3 and maintained in coaxial relationship therewith, by insulators 2 I. Preferably, the insulators are located at each point where the diameter of conductor 12 is changed. Thus any disturbance in the impedance due to the presence of the insulators may be com pensated for by proper proportioning of the immediatel preceding section. Furthermore, the quarter Wave spacing of the insulators assures that each insulator compensates for the effect of its neighbor. When the spacing of the radiators is other than a quarter wave the insulators are preferably arranged in pairs, the insulators of each pair being spaced apart a quarter wavelength or odd multiple thereof. The outer shell i5 is provided with a plurality of apertures l4 through which the radiators l0 pass. The outer shell is is fastened to a conductive ground plate or metallic sheet 25 along the side opposite the apertures i l. The coaxial line and a part of each of the radiators are enclosed within a continuous Weather shield I8. The shield I8 is preferably of some plastic insulating material, such as a polymerized styrene or a methyl methacrylate plastic having the low losses at high frequencies. The plastic shield helps to streamline the antenna and eliminates the need of bushings in apertures M on the shell of the coaxial line 15. Small rubber bushings 20 are, however, provided where the radiators penetrate the plastic shell ill in order to weatherproof the structure. The ends of the plastic shield l8 are closed by end plates l9. An intermediate section of transmission line I6 is provided between the antenna section and the transmission line I5 so that the impedance of the antenna. is transformed to a value equal to the impedance of the transmission line.

The directivity pattern of the antenna shown in Figures 1 and 2 mounted on a conductive sheet 6 ft. by 8 ft. in dimensions and operating on a frequency in the vicinity of 500 megacycles is shown in Figure 3 by curve 30. The reference plane is the plane in which radiators It all lie. It will readily be seen by an inspection that the directivity pattern is quite sharp and has no large secondary lobes or cars. The gain of the antenna along the line of maximum radiation of 3 curve 38 as compared to a dipole mounted in free space is '7.

Figure 4, pattern 40, shows the directivity obtained with the same antenna, in this case, how ever, mounted on a conductive sheet having dimensions of the order of 6 ft. by 18 ft. The gain over a free space dipole a indicated by comparison measurements is of the order of 10, a considerable increase over that shown in Figure 3.

The pattern 50 of Figure 5 indicates the direc tivity obtained when the forward portion of the conductive sheet 25 is replaced by a curved portion 55 (Figure 6) of 27 inch radius. Sheet 25 is otherwise of the dimensions used for obtaining the curve of Figure 3. It will be noted that the back radiation increases somewhat with this arrangement.

In Figure 7 is shown the band width curve obtained while matching the input impedance of the antenna to the associated transmission line. In curve 10 percentage of reflection is plotted against frequency of operation. It will be noted that this type of antenna is very good with respect to band width, the percentage of reflection remaining under 10 percent from 377 megacycles to something over 400 megacycles. Thi characteristic of the antenna was also indicated during tests for determination of the radiation pattern when it was discovered that the length of each of the radiators could be varied by as much as of an inch without any measurable effects on the pattern.

While I have particularly shown and described several modifications of my invention, it is to be distinctly understood that my invention is not limited thereto but that improvements within the scope of the invention may be made.

I claim:

1. A directive antenna system including a row of radiators arranged parallel to one another in a single plane, said radiators being so spaced that the direction of maximum response of said system lies substantially in a line normal to the axis of said radiator, said radiators being coupled at equal intervals along a transmission line carrying high frequency energy, said couplings being such that the energy on such line is divided equally among said radiators, the dimensions of said transmission line varying along its length to provide a characteristic impedance which increases in a predetermined manner from one end to the other.

2. A directive antenna system including a row of radiators arranged parallel to one another in a single plane, said radiators being o spaced that the direction of maximum response of said system lies substantially in a line normal to the axis of said radiators, said radiators being coupled at equal intervals along a transmission line carrying high frequency energy, said coupling being such that the energy on said line is divided equally among said radiators, the dimensions of said transmission lines varying along its length, the variation being such that, progressing along the length of said line at each coupling point of a radiator to said line, the impedance of the immediately preceding section is equal to the combined impedance of the radiator coupled thereto and the following portion of the system.

3. A directive antenna system including a transmission line having a pair of conductors, means for coupling a transducer to one end of transmission line, radiator elements connected to one of said conductors at spaced points along said line, the dimensions of said transmission line being so varied along the length of said line that, progressing along said line from said coupling means toward the other end at each junction point between one of said conductors and a radiator element, the impedance of the immediately preceding section of the transmission line is equal to the combined impedance of the radiator and the following portion of the system.

4. A directive antenna system including a transmission line having a pair of conductors, means for coupling a transducer to one end of said line, radiator elements connected to one of said conductors at spaced points along said line, the spacing between said conductors being so increased at each junction of a radiator with one of said conductors, progressing along the length of said line in a direction away from said coupling means, that at each junction the impedance of the immediately preceding section is equal to the combined impedance of the radiator and the following portion of the system.

5. A directive antenna system including a transmission line having a pair of conductors, means for coupling a transducer to one end of said line, radiator elements connected to one of said conductors at points spaced along said line a distance equal to a quarter of the operating wave length, the spacing between said conductors being so increased at each junction of a radiator with one of said conductors, progressing along the length of said line in a direction away from said coupling means, that at each junction the impedance of the immediately preceding section is equal to the combined impedance of the radiator and the following portion of the system.

6. A directive antenna system including a transmission line having an outer shell and a tapered inner conductor, means for coupling a transducer to one end of said transmission line, radiator elements connected to said inner conductor at points spaced along said line a distance equal to a quarter of th operating wavelength, the taper of said inner conductor being such that, progressing along said line from said coupling means toward the other end at each junction point between said inner conductor and radiator element, the impedance of the immediately preceding section of transmission line is equal to the combined impedance of the radiator and the following portion of the system.

7. A directive antenna system including a transmission line having an outer shell and a tapered inner conductor, means for coupling a transducer to one end of said transmission line, radiator elements connected to said inner conductor at points spaced along said line a distance equal to a quarter of the operating wavelength, the taper of said inner conductor being such that, progressing along said line from said coupling means toward the other end at each junction point between said inner conductor and radiator element, the impedance of the immediately preceding section of transmission line is equal to the combined impedance of the radiator and the following portion of the system, said radiators passing through apertures in said outer line and lying in a plane along the length of said shell.

8. A directive antenna system including a transmission line having an outer shell and a tapered inner conductor, means for coupling a transducer to one end of said transmission line, radiator elements connected to said inner conductor at points spaced along said line a distance equal to a quarter of the operating wavelength, the taper of said inner conductor being such that,

progressing along said line from said coupling means toward the other end at each junction point between said inner conductor and radiator element, the impedance of the immediately preceding section of transmission line is equal to the combined impedance of the radiator and the following portion of the system, said radiators passing through apertures in said outer line and lying in a plane along the length of said shell and an insulating V-shaped shield covering said line and at least a part of the radiator.

9. A directive antenna system including a transmission line having an outer shell and an inner conductor, means for coupling a transducer to one end of said line, radiator elements connected to said inner conductor at points spaced along said line a distance equal to a quarter of the operating wavelength, said inner conductor being so reduced in diameter at each junc tion of a radiator therewith, progressing along the length of said line in the direction away from said coupling means that at each junction the impedance of th immediately preceding section REFERENCES CITED lhe following references are of record in the file of this patent:

UNITED STATES PATENTS 20 Number Name Date 1,821,402 Peterson Sept. 1, 1931 2,236,393 Beck et a1. Mar. 25, 1941 2,286,179 Lindenblad June 9, 1942 

